Issue now resolved thanks to great customer support from EUK again.
For anyone with similar problems in the future, what happens when you change the A Record of a domain with another registrant so it points to your EUK server IP and add an addon domain for that domain from cPanel is that cPanel by default, drops the addon domain into the local domains file. It needs to go into the remote domains file though as the domain needs to use an external server for emails ( in my case anyway, as I only wanted to host the website and not the email accounts ). This needs to be done by EUK support as they need to configure the settings on your behalf.
All working fine now folks, many thanks once again.
